While larger glass and plastic bottles (e.g., 32 ounce and larger) with handles are widely used they have drawbacks in manufacture and in use.
With respect to large plastic bottles with handles for lifting, carrying and pouring, they generally are made by the extrusion blow molding process.
In this process an extruder initially forms large diameter preforms, hollow tubes known as parisons, and the parisons are positioned within blow molds having the desired final shape of the bottles. In each blow mold a portion of the parison is pinched off to form a handle shape and the pinched parison is blown to its final bottle dimensions with a hollow handle and an interconnecting web. Thereafter, the web is removed to provide a handle for gripping, lifting, carrying and pouring.
In forming such hollow handles relatively high plastic temperatures and substantial parison thicknesses are required to provide satisfactory fusion in the pinched and blown parison. Also, the parison must have a large enough diameter so that it will essentially traverse the breadth of the bottle when pinched and blown.
The procedures for forming these bottles are well known. See Modern Plastics Encyclopedia, Vol. 54, No. 10A, 1977-1978, McGraw-Hill Publishing Co. (e.g., section on "Blow Molding" at page 230, et seq.; also see section on "Injection Blow Molding" at page 232 et seq.).
Depending on the design, the pinched, blown hollow handle can provide ease in carrying, lifting and pouring, or simply ease in carrying and lifting. In the instance of a pouring handle, moreover, the need to grip the side walls of the container is eliminated. This can result in lighter weight bottles at lower costs. These and other features make the pouring handle very popular for large plastic bottles made from a wide variety of thermoplastic materials including polyolefins (polyethylene and polypropylene) and polyvinyl chloride.
However, these methods and the resulting bottles with hollow handles do have shortcomings. For example, decreasing the amount of plastic, used to form the bottles, known as "light weighting", is limited in many cases by the need for adequate parison thickness to provide the requisite fusion along the extensive pinched off areas.
Another limitation is that the required large diameter parison produces bottles having wide variations in wall thicknesses, especially at and near the sidewall at the bottom juncture and at the shoulder area--the most vulnerable areas to drop impact and denting forces. This results because the pinch off distributes the parison into thick areas at each end of the pinch off and in very thin areas in the blown bottle at right angles to it.
Still another limitation is that the relatively high fusion temperatures required to form the pinched off hollow handles cannot be used to form handles in the newer stretch blow molding process for forming plastic bottles. This process differs from the hollow handle blow molding process in that the parison is first stretched and then blown while at temperatures which are much lower than the fusion temperatures, generally within the 100.degree. F. range above T.sub.g (the temperature at which the plastic material passes from the glass phase to the rubber phase). This procedure, which is known as stretch blow molding, or orientation blow molding, is not only replacing earlier blow molding techniques, but is opening up new markets. Advantages of the new procedures are related to the biaxial orientation of the polymeric material. While the parison is at a temperature insufficient to permit free plastic flow it is expanded biaxially to conform with the blow mold. The temperature of operation generally within the 100.degree. F. range immediately above T.sub.g is such that expansion introduces true strain into the material, and this strain is translated into a definable polymer orientation which results in a number of attributes.
Alignment of polymer molecules results in increased tensile strength, as well as increased clarity, increased impact strength, and reduced creep. A vast market for carbonated soft drink containers is a direct result of significantly improved gas barrier properties.
Suitable container materials for stretch blow molding are substituted and unsubstituted thermoplastic hydrocarbons. Commonly used materials at this time include acrylonitrile polymers, polyvinyl chloride, polyethylene terephthalate, and polypropylene. This newer procedure also is known. See Modern Plastics Encyclopedia, Vol. 54, No. 10A, 1977-1978, McGraw-Hill Publishing Co. (e.g., section on "Stretch-Blow Molding" at page 233 et seq.).
Of the above commonly used materials for stretch-blow molding, polyethylene terephthalate possesses an additional beneficial processing characteristic in that, while it is being stretched at biorientation temperatures, the non-crystalline polymer crystallizes. This greatly increases its resistance to further stretching. The result is a much more uniform wall thickness, even in bottle shapes which otherwise are noted for poor wall thickness distribution.
The problem with producing plastic containers with handles using the stretch blow processes results from the nature of the process and condition of the plastic at the time it is biaxially oriented. First, it is not possible to produce handles by the aforementioned parison pinch-off technique because the plastic temperature required for suitable molecular orientation is much too low to permit adequate fusion of the plastic. To initially form the handle at elevated temperatures and then to cool to biorientation temperatures before stretching and blowing would yield handles, and substantial other unoriented portions of the container, with inferior containment and other properties. Further, the large diameter parison required for the parison pinch-off technique reduces the amount of desired biorientation.
With respect to producing both plastic and glass bottles with handles, moreover, difficulty has been encountered in locating the handle in other than the uppermost portion of the bottle. To achieve optimum balance when pouring, however, it is more desirable from a handling standpoint to, in most instances, place the handle in a more central position on the sidewall of the bottle. At present only extrusion blow molding processes with their already discussed shortcomings may be used to form such bottles and handles. Glass and other plastic blow molding processes require that the handle be located on the uppermost region of the bottle because the handle must be formed in the mold for the preform or parison before expansion in the blow mold.
Thus, there is a need for new and improved bottles with handles and for new and improved methods for forming such bottles.